Sixty patients with cerebral ischemia were studied by both CT and angiography. The results are: 1. Thrombosis of the internal carotid artery: CT shows a hypodensity lateral to the frontal horn. 2. Thrombosis of the middle cerebral artery: the hypodensity occupies the convexity of the frontal, parietal, and temporal lobes. 3. In thrombosis of the posterior cerebral artery there is an occipital hypodensity, while in thrombosis of the vertebral artery the hypodensity occupies a cerebellar hemisphere. 4. Circulatory disturbances without occlusion of the major cerebral vessels: there is a disproportion between the serious CT lesion and paucity of the angiographic findings.